ACC.01: Guidelines for Internal Inspection of Air-Cooled Condensers

Dr. A. G. Howell, Gary Bishop, David Rettke, Rene Villafuente, Dr. R.B. Dooley, Hoc Phung
Original Issue: May 12, 2015. Revision due: May 12, 2018. Publication in whole or in part is allowed provided that attribution is given to the Air Cooled Condenser Users Group.
The employment of air-cooled condensers (ACCs) in fossil fueled power-generating facilities has increased dramatically early in the 21st century. These condensers are massive structures at power plant sites, because a large cooling surface is required to compensate for the relatively poor heat capacity of air, in comparison with that of water. As experience has been gained in operating and maintaining facilities with ACCs, it has become clear that corrosion of steam-side surfaces can be a significant problem for unit operation. In particular, iron oxide transport can introduce a large quantity of contaminants to the condensate / boiler feedwater, and through-wall penetrations of cooling tubes can cause significant air inleakage, potentially leading to reduced condenser performance and permitting ingress of air.

Corrosion in Air Cooled Condensers – Understanding and Mitigating the Mechanisms

Setsweke Phala, Denis Aspden, Dr Francois du Preez, Hein Goldschagg, and Keith Northcott
Presented at API PowerChem 2008, Queensland, Australia.
Corrosion in the air cooled condensors has been a cause for concern for several years in Eskom’s direct dry cooling stations. The exact mechanism of the observed corrosion has not been positively identified but is thought to be a form of flow accelerated corrosion.
Eskom has over the years tried several methods to mitigate the corrosion, such as varying the steam/condensate pH as well as the application of certain so-called protective epoxy coatings. There is clearly a link between the observed corrosion and the prevailing pH. Studies have shown a lower rate of iron transport as the pH has been increased, but this has also had an impact on the operation of the condensate polishers. Significant differences in the nature and extent of corrosion of air cooled condensers have been observed between base loaded and two shift operation of these plants.
Research, including international collaboration continues to develop a better understanding of the corrosion mechanisms at play, together with strategies to best mitigate the corrosion and ensure design life is achieved.
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